RTEMS has been providing a real time, multi threaded, POSIX API on embedded systems for decades. It's got preemption, interactive shells, a libbsd port with net

RTEMS has been providing a real time, multi threaded, POSIX API on embedded systems for decades. It's got preemption, interactive shells, a libbsd port with networking, etc. It's popular in spacecraft, especially in combination with NASA's Core Flight System (cFS). I've run it on an STM32F4 and a Raspberry Pi. BSP support is a little lacking in some cases. The raspberry pi is currently crashing on a call to fflush(). No idea why. I really wish more people knew about it. As a matter of fact, I'll post about it here.